[dgemm]

The theoretical best latency would be something like speed_of_light_in_fiber/great_circle_distance_between_regions, both of which are pretty easy to find. The first is a constant you can look up, and the second you can compute from coordinates of each region pair.

[CountVonGuetzli]

Thats what we did as well, via wolfram alpha. I.e. we were too lazy to look up everything ourselves and just asked it straight up how long of a roundtrip it would be between two destinations via fiber. We checked one result and it was spot on. This was six years ago tho